Method of drying paper to produce a cockle finish



July 6, 1965 G. R. DONELSON METHOD OF DRYING PAPER TO PRODUCE A COGKLE FINISH Filed Nov. 28, 1961 FIGI FIGZ INVENTOR.

GEORGE ROBERT DONELSON MY WM,

ATTORNEYS United States Patent 3,193,403 NIETHGD 0F DRYING PAPER T0 PRODUCE A (BUCKLE FINISH George Robert Donelson, Adams, Mass, assignor, by

mesne assignments, to The Budd Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 28, 1961, Ser. No. 155,302 2 Claims. (Cl. 117-7) This invention relates to the production of a cockle finish on a sized erasable paper. To obtain such a finish, the coated paper sheet must be air-dried in such a way as to permit shrinkage in all directions. The coating material applied to paper webs is apt to be sticky when Wet so that there are practical limits to the viscosity and quantity of coating applied to a paper sheet which must be observed if excessive sticking of the sheet to rolls in the drier is to be avoided. This is especially true of coating compositions containing casein or glue as a principal ingredient.

I have discovered that in the drying process, the coating ceases to be sticky after its moisture content decreases to a percentage below a figure which can be experimentally determined for any given composition, and that cockling of the sheet does not begin until the moisture content is much less than the critical point for non-sticking.

According to the present invention, a paper sheet is sized, then pre-dried at a comparatively high temperature and under tension until its moisture content is below the critical point for non-sticking, then is further air-dried at a lower temperature and free from tension to produce the cockle finish.

For a more complete understanding of the invention, reference may be had to the following description thereof, and to the drawing of which FIGURE 1 is a diagrammatic elevational View of the supply end portion of an apparatus for practicing the invention; and

FIGURE 2 is a similar view of the remaining portion of the apparatus.

A web of paper W, such as bond paper, is drawn from a supply roll on a revolvable loading frame 11 and is guided into a size press 12 by which the web becomes coated with a sizing composition supplied in a container 14. The composition employed may, for example, be a casein size such as is described in Patent No. 1,994,750. The freshly coated paper is then floated through a predrying chamber 16 in which it is supported by jets of air heated to a temperature of 280300 F., the jets keeping the web out of contact with the apparatus during its passage through the chamber. A pre-drier of this type is illustrated in US. Patent No. 927,995. Considerable tension is maintained on the paper in the drying chamber 16 by a weighted dance roll 18 located in a loop of the web just after the web leaves the pre-drier 16. The pre-drier 16 is adjusted so that when the web leaves it, the moisture content of the web is below the critical percentage for non-sticking. The paper is in the chamber a suflicient time to reduce its moisture content below the critical percentage for non-sticking. The percentage when casein sizing is used has been found to be between 36% and 39%. The web is then further dried in a Barber drier 20 in which the web passes over nonheated rolls in air which at the entrance is maintained at a temperature of about 210 F. The drier 20 contains groups of rolls, e.g., six groups, each group having upper rolls 22 and lower rolls 24 some or all of which may be driven. The web passes alternately under the lower rolls and over the upper rolls, a light but controlled tension on the web being maintained by dance rolls 26 between "ice successive groups, the dance rolls being counter-weighted to lighten their weight pressing down on the loops of web passing under them. When the web enters the Barber drier, it is dry enough to pass over and under rolls without sticking to them but is moist enough to cockle properly if the remainder of the drying operation is carried out While the web is under little or no tension so that it can shrink in all directions to produce the cockled finish. Since the cockling process does not begin until the moisture content is less than 17% (usually about 11%), the partially dried web from the pre-drier will cockle just as well as will a web coming direct from the size press, but will not stick to the rolls. This eliminates delays in operation which have heretofore been necessitated by the coating materials sticking to the rolls of the drier. The resulting freedom from interruptions in the operation of the machine for the purpose of cleaning the rolls materially increases production. Furthermore, the drying operation is done in a single pass when certain coating compositions are employed, this resulting in a further increase in production. Also avoided is wrinkling of the paper web which has often resulted from the web sticking to the rolls. A further advantage flowing from the pre-drying is that a wider latitude is had in the viscosity of the coating composition employed and the permissible thickness of the films of coating composition on the web.

When the web leaves the Barber drier, it is rolled up on a mandrel at 28 in the usual manner.

I claim:

1. The method of producing an improved cockle finish on a paper web with a wet sizing composition which becomes sticky during drying, the web being of the type which does not shrink uniformly when continuously subjected during drying to tensions exceeding a predetermined magnitude;

(a) wetting the web by application of a wet-sizing casein composition and increasing the moisture content of the web to an initial value greater than 36% by weight at which sticking defects are prevented by the presence of excess moisture;

(b) predrying the wet web in a first dryer with the web supported by a plurality of jets of heated air and maintained under a first tension greater than said predetermined magnitude and suflicient to advance the web through the dryer free of mechanical contact within the dryer and simultaneously reducing the moisture content of the web from said initial value to an intermediate value between 17 and 11% by weight at which sticking defects are prevented by the lack of sufiicient moisture;

(c) and thereafter completing drying of the web in a second dryer with the web mechanically supported and maintained under a second tension less than the predetermined magnitude whereby uniform cockling is produced without surface defects due to sticking.

2. The method of producing an improved cockle finish on a paper web with a wet sizing composition which becomes sticky during drying, the web being the type which does not shrink uniformly when continuously subjected during drying to tensions exceeding a predetermined magnitude, which method comprises the steps of:

(a) wetting the web by application of a wet-sizing composition and increasing the moisture content of the web to an initial value at which sticking defects are prevented by the presence of excess moisture;

(b) predrying the wet web in a first dryer with the web supported by a plurality of jets of heated air and maintained under a first tension greater than said predetermined magnitude and sufiicient to ad vance the web through the dryer free of mechanical 9 5 contact Within the dryer and simultaneously reducing the moisture content of the web from said initial value to an intermediate value at which sticking defects are prevented by the lack of sufficient moisture; and V (c) thereafter" completing drying of the web in a second dryer with the web mechanically supported and maintained under a second tension less than the predetermined magnitude whereby uniform cockling is produced without surface defects due to sticking.

Morrow 34-156 Callan 117-156 Van Deroef et a1. 11867X Shaw 1l71l9.8

Stafford 1171l RICHARD D. NEVIUS, Primary Examiner. 

1. THE METHOD OF PRODUCING AN IMPROVED COCKLE FINISH ON A PAPER WEB WITH A WET SIZING COMPOSITION WHICH BECOMES STICKY DURING DRYING, THE WEB BEING OF THE TYPE WHICH DOES NOT SHRINK UNIFORMLY WHEN CONTINUOUSLY SUBJECTED DURING DRYING TO TENSIONS EXCCEDING A PREDETERMINED MAGNITUDE; (A) WETTING THE WEB BY APPLICATION OF A WET-SIZING CASEIN COMPOSITION AND INCREASING THE MOISTURE CONTENT OF THE WEB TO AN INITIAL VALUE GREATER THAN 36% BY WEIGHT AT WHICH STICKING DEFECTS ARE PREVENTED BY THE PRESENCE OF EXCESS MOISTURE; (B) PREDRYING THE WET WEB IN A FIRST DRYER WITH THE WEB SUPPORTED BY A PLURALITY OF JETS OF HEATED AIR AND MAINTAINED UNDER A FIRST TENSION GREATER THAN SAID PREDETERMINED MAGNITUDE AND SUFFICIENT TO ADVANCE THE WEB THROUGH THE DRYER FREE OF MECHANICAL CONTACT WITHIN THE DRYER AND SIMULTANEOUSLY REDUCING THE MOISTURE CONTENT OF THE WEB FROM SAID INITIAL VALUE TO AN INTERMEDIATE VALUE BETWEEN 17% AND 11% BY WEIGHT AT WHICH STICKING DEFECTS ARE PREVENTED BY THE LACK OF SUFFICIENT MOISTURE; (C) AND THEREAFTER COMPLETING DRYING OF THE WEB IN A SECOND DRYER WITH THE WEB MECHANICALLY SUPPORTED AND MAINTAINED UNDER A SECOND TENSION LESS THAN THE PREDETERMINED MAGNITURE WHEREBY UNIFORM COCKLING IS PRODUCED WITHOUT SURFACE DEFECTS DUR TO STICKING. 